The present invention relates generally to wavelength division multiplexing and, more particularly, to wavelength division multiplexing/demultiplexing devices employing patterned optical components.
Optical communication technology relies on wavelength division multiplexing (WDM) to provide increased bandwidth over existing installed fiber, as well as newly deployed fiber installations. Several technologies exist to provide the technical solution to WDM: array waveguide gratings (AWG""s), fiber Bragg grating based systems, interference filter based systems, Mach-Zehnder interferometric based systems, and diffraction grating based systems, to name a few. Each system has advantages and disadvantages over the others.
Diffraction grating based systems have the advantage of parallelism, which yields higher performance and lower cost for high channel count systems. One drawback to traditional diffraction grating based systems, however, is an insertion loss that rises quickly and monotonically as the source illumination drifts off of the center of the desired communication channel wavelength. That is, traditional diffraction grating based systems invariably suffer from a variation in transmission efficiency across a wavelength channel. This variation in transmission efficiency with wavelength creates deleterious effects on modulated signals. For analog signals it creates harmonic distortion, for digital signals it increases the bit-error-rates at higher modulation bandwidths.
Also, most traditional diffraction grating based systems have an inherently gaussian-shaped passband profile. Such a gaussian-shaped passband profile is generally very narrow with a single peak and steep passband edges. Thus, even when a communication channel drifts off of its center wavelengths by only a slight amount, signal coupling with a receiving fiber is often severely detrimentally affected.
One attempt to alleviate at least one aspect of the above-described shortcomings is described by D. Wisely in xe2x80x9cHigh Performance 32 Channel HDWDM Multiplexer with 1 nm Channel Spacing and 0.7 nm Bandwidthxe2x80x9d, SPIE, Vol. 1578, Fiber Networks for Telephony and CATV (1991). In this paper, Wisely suggests that a microlens may be employed at the end of an input fiber in a WDM device so as to widen the gaussian-shaped passband profile of the WDM profile. That is, by widening the gaussian-shaped passband profile of the WDM device, there is less susceptibility to wavelength drift in communication channels. However, widening the gaussian-shaped passband profile of a WDM device may increase the chances of channel crosstalk. Thus, a tradeoff determination must be made when deciding whether or not to implement the above-described technique of Wisely.
Another attempt to alleviate at least one aspect of the above-described shortcomings is described by Martin et al. in U.S. Pat. No. 6,084,695. In this patent, Martin et al. suggest that a converging lens array, which is disclosed to be a planar microlens array with an index gradient, may be used to increase the width of elementary bands, and thereby increase the ratio between the width of elementary bands and the distance separating the central wavelengths of adjacent elementary bands in a multiplexer/demultiplexer device. Each microlens in the planar microlens array corresponds to a respective input/output fiber, which is placed directly in the focal point of its corresponding microlens. Thus, the apparent diameter of a beam exiting/entering the core of an input/output fiber as seen by a dispersion element or grating of the multiplexer/demultiplexer devices is the diameter of the beam as it is incident upon a corresponding microlens, and not the actual diameter of the beam as it exits/enters the core of the input/output fiber. That is, the width of each elementary band as seen by the dispersion element or grating of the multiplexer/demultiplexer device is increased without increasing the distance separating the central wavelengths of adjacent elementary bands.
However, as with the Wisely reference described above, the widening of elementary passbands as disclosed by Martin et al. may increase the chances of channel crosstalk. Also, Martin et al. disclose that an additional fiber (not shown) is required once for each channel wavelength or once for the multiplexed output beam of the multiplexer/demultiplexer device to attenuate the peak of each passband and thereby flatten each passband. Furthermore, Martin et al. disclose that the spacing between the input/output fibers, as well as the spacing between microlenses, is equal so as to allow for a much simpler implementation of the multiplexer/demultiplexer device. However, Martin et al. additionally disclose that this equal spacing of the input/output fibers and the microlenses is achieved only through the use of a prism, which compensates for wavelength spacing non-linearity due to dispersion laws of the dispersion element or grating. Thus, a tradeoff determination and additional device complexities are encountered when deciding whether or not to implement the above-described multiplexer/demultiplexer device of Martin et al.
While no other known attempts have been made to alleviate one or more aspects of the above-described shortcomings, it is presumed that such other attempts, if made, would also require certain tradeoffs to be made and/or complexities to be added. Thus, in view of the foregoing, it would be desirable to provide a WDM device which overcomes the above-described inadequacies and shortcomings with minimal or no tradeoffs or additional complexities.
The primary object of the present invention is to provide wavelength division multiplexing/demultiplexing devices which overcome the above-described inadequacies and shortcomings with minimal or no tradeoffs or additional complexities.
The above-stated primary object, as well as other objects features, and advantages, of the present invention will become readily apparent to those of ordinary skill in the art from the following summary and detailed descriptions, as well as the appended drawings. While the present invention is described below with reference to preferred embodiment (s), it should be understood that the present invention is not limited thereto. Those of ordinary skill in the art having access to the teachings herein will recognize additional implementations, modifications, and embodiments, as well as other fields of use, which are within the scope of the present invention as disclosed and claimed herein, and with respect to which the present invention could be of significant utility.
According to the present invention, improved wavelength division multiplexing/demultiplexing devices are provided. In the case of an improved wavelength division multiplexing device having a diffraction grating for combining a plurality of narrowband optical beams into a multiplexed, polychromatic optical beam, wherein the plurality of narrowband optical beams are received from a corresponding plurality of optical sources and the multiplexed, polychromatic optical beam is transmitted to a corresponding optical receiver, the improvement comprises employing a plurality of patterned optical input components corresponding to the plurality of narrowband optical beams and the plurality of optical sources for introducing a first patterned phase delay into the plurality of narrowband optical beams, wherein each of the plurality of patterned optical input components has an effective focal length such that each of the plurality of optical sources is disposed substantially inside the effective focal length of a corresponding one of the plurality of patterned optical input components. The improvement also comprises employing a patterned optical output component corresponding to the multiplexed, polychromatic optical beam and the optical receiver for introducing a second patterned phase delay into the multiplexed, polychromatic optical beam, wherein the patterned optical output component has an effective focal length such that the optical receiver is disposed substantially inside the effective focal length of the patterned optical output component. The first patterned phase delay and the second patterned phase delay are added so as to reshape the passband of the improved wavelength division multiplexing device.
In accordance with other aspects of the present invention, the effective focal length of each of the plurality of patterned optical input components may be the same. Also, the effective focal length of the patterned optical output component may be the same as the effective focal length of each of the plurality of patterned optical input components. Alternatively, the effective focal length of each of the plurality of patterned optical input components may differ. Also, the effective focal length of the patterned optical output component may differ from the effective focal length of each of the plurality of patterned optical input components. In any event, the effective focal length of each of the plurality of patterned optical input components is beneficially derived from a quadratic phase term that is inherent in each of the plurality of patterned optical input components. Similarly, the effective focal length of the patterned optical output component is beneficially derived from a quadratic phase term that is inherent in the patterned optical output component.
In accordance with further aspects of the present invention, at least some of the plurality of patterned optical input components and the patterned optical output component are beneficially formed on a common substrate.
In accordance with still further aspects of the present invention, the spacing between each of the plurality of optical source, as well as the spacing between each of the corresponding plurality of patterned optical input components, increases as the difference between the wavelengths associated with each of the plurality of narrowband optical beams being received from corresponding ones of the plurality of optical sources increases.
In accordance with still further aspects of the present invention, each of the plurality of optical sources may be, for example, an optical input fiber or a laser diode. If each of the plurality of optical sources is an optical input fiber, wherein each of the plurality of narrowband optical beams is received from a corresponding one of the plurality of optical input fibers, each of the plurality of optical input fibers is beneficially disposed from a corresponding one of the plurality of patterned optical input components at a distance defined by:   x  =            f      2        +                  1        4            ·                                    4            ·                          f              2                                -                                                    π                2                            ·                              do                4                                                    λ              2                                          
wherein f is the effective focal length of the corresponding one of the plurality of patterned optical input components, do is a Gaussian mode field diameter of the optical input fiber, and xcex is the wavelength associated with the narrowband optical beam being received from the optical input fiber. Accordingly, the distance between each of the plurality of optical input fibers and each corresponding one of the plurality of patterned optical input components may vary with wavelength. Alternatively, the effective focal length of each of the plurality of patterned optical input components may differ so that the distance between each of the plurality of optical input fibers and each corresponding one of the plurality of patterned optical input component does not vary with wavelength.
In accordance with still further aspects of the present invention, the optical receiver is beneficially an optical output fiber, wherein the multiplexed, polychromatic optical beam is transmitted to the optical output fiber. The optical output fiber is beneficially disposed from the corresponding patterned optical output component at a distance defined by:   x  =            f      2        +                  1        4            ·                                    4            ·                          f              2                                -                                                    π                2                            ·                              do                4                                                    λ              2                                          
wherein f is the effective focal length of the corresponding patterned optical output component, do is a Gaussian mode filed diameter of the optical output fiber, and xcex is the average wavelength associated with the multiplexed, polychromatic optical beam being transmitted to the optical output fiber.
In accordance with other aspects of the present invention, the plurality of patterned optical input components beneficially comprises a plurality of patterned phase masks for introducing the first patterned phase delay into the plurality of narrowband optical beams. Each of the plurality of patterned phase masks is preferably formed on/in a corresponding collimating microlens. Alternatively, the plurality of patterned optical input components also beneficially comprises a plurality of collimating microlenses for collimating the plurality of narrowband optical beams. In either case, each corresponding collimating microlens or each of the plurality of collimating mircolenses contributes to a widening of the passband of the improved wavelength division multiplexing device.
In accordance with further aspects of the present invention, each of the plurality of patterned phase masks beneficially has a periodic phase profile. A benefit to this aspect is that the passband of the improved wavelength division multiplexing device is typically a gaussian-shaped passband having a peak, and the periodic phase profile of each patterned phase mask contributes to a flattening of the peak of the gaussian-shaped passband of the improved wavelength division multiplexing device. Another benefit to this aspect is that the passband of the improved wavelength division multiplexing device is a guassian-shaped passband having sideband slopes, and the periodic phase profile of each patterned phase mask contributes to a steepening of the sideband slopes of the gaussian-shaped passband of the improved wavelength division multiplexing device.
In accordance with still further aspects of the present invention, each of the plurality of patterned phase masks beneficially has a non-periodic phase profile. A benefit to this aspect is that the passband of the improved wavelength division multiplexing device is a guassian-shaped passband having a peak, and the non-periodic phase profile of each patterned phase mask contributes to a flattening of the peak of the gaussian-shaped passband of the improved wavelength division multiplexing device. Another benefit to this aspect is that the passband of the improved wavelength division multiplexing device is a guassian-shaped passband having sideband slopes, and the non-periodic phase profile of each patterned phase mask contributes to a steepening of the sideband slopes of the guassian-shaped passband of the improved wavelength division multiplexing device.
In accordance with other aspects of the present invention, the patterned optical output component beneficially comprises a patterned phase mask for introducing the second patterned phase delay into the multiplexed, polychromatic optical beam. The patterned phase mask is preferably formed on/in a focusing microlens. Alternatively, the patterned optical output component also beneficially comprises a focusing microlens for focusing the multiplexed, polychromatic optical beam. In either case, the focusing microlens contributes to a widening of the passband of the improved wavelength division multiplexing device.
In accordance with further aspects of the present invention, the patterned phase mask beneficially has a periodic phase profile. A benefit to this aspect is that the passband of the improved wavelength division multiplexing device is a guassian-shaped passband having a peak, and the periodic phase profile of the patterned phase mask contributes to a flattening of the peak of the guassian-shaped passband of the improved wavelength division multiplexing device. Another benefit to this aspect is that the passband of the improved wavelength division multiplexing device is a guassian-shaped passband having sideband slopes, and the periodic phase profile of the patterned phase mask contributes to a steepening of the sideband slopes of the gaussian-shaped passband of the improved wavelength division multiplexing device.
In accordance with still further aspects of the present invention, the patterned phase mask beneficially has a non-periodic phase profile. A benefit to this aspect is that the passband of the improved wavelength division multiplexing device is a guassian-shaped passband having a peak, and the non-periodic phase profile of the patterned phase mask contributes to a flattening of the peak of the gaussian-shaped passband of the improved wavelength division multiplexing device. Another benefit to this aspect is that the passband of the improved wavelength division multiplexing device is a guassian-shaped passband having sideband slopes, and the non-periodic phase profile of the patterned phase mask contributes to a steepening of the sideband slopes of the gaussian-shaped passband of the improved wavelength division mutliplexing device.
In the case of an improved wavelength division demultiplexing device having a diffraction grating for separating a multiplexed, polychromatic optical beam into a plurality of narroband optical beams, wherein the multiplexed, polychromatic optical beam is received from a corresponding optical source and the plurality of narrowband optical beams are transmitted to a corresponding plurality of optical receivers, the improvement comprises employing a patterned optical input component corresponding to the multiplexed, polychromatic optical beam and the optical source for introducing a first patterned phase delay into the multiplexed, polychromatic optical beam, wherein the patterned optical input component has an effective focal length such that the optical source is disposed substantially inside the effective focal length of the patterned optical input component. The improvement also comprises employing a plurality of patterned optical output components corresponding to the plurality of narrowband optical beams and the plurality of optical receivers for introducing a second patterned phase delay into the plurality of narrowband optical beams, wherein each of the plurality of patterned optical output components has an effective focal length such that each of the plurality of optical receivers is disposed substantially inside the effective focal length of a corresponding one of the plurality of patterned optical output components. The first patterned phase delay and the second patterned phase delay are added so as to reshape the passband of the improved wavelength division demultiplexing device.
In accordance with other aspects of the present invention, the effective focal length of each of the plurality of patterned optical output components may be the same. Also, the effective focal length of the patterned optical input component may be the same as the effective focal length of each of the plurality of patterned optical output components. Alternatively, the effective focal length of each of the plurality of patterned optical output components may differ. Also, the effective focal length of the patterned optical input component may differ from the effective focal length of each of the plurality of patterned optical output components. In any event, the effective focal length of each of the plurality of patterned optical output components is beneficially derived from a quadratic phase term that is inherent in each of the plurality of patterned optical output components. Similarly, the effective focal length of the patterned optical input component is beneficially derived from a quadratic phase term that is inherent in the patterned optical input component.
In accordance with further aspects of the present invention, at least some of the plurality of patterned optical output components and the patterned optical input component are beneficially formed on a common substrate.
In accordance with still further aspects of the present invention, the spacing between each of the plurality of optical receivers, as well as the spacing between each of the corresponding plurality of patterned optical output components, increases as the difference between the wavelengths associated with each of the plurality of narrowband optical beams being transmitted to corresponding ones of the plurality of optical receivers increases.
In accordance with still further aspects of the present invention, each of the plurality of optical receivers may be, for example, an optical output fiber or a photodiode. If each of the plurality of optical receivers is an optical output fiber, wherein each of the plurality of narrowband optical beams is transmitted to a corresponding one of the plurality of optical output fibers, each of the plurality of optical output fibers is beneficially disposed from a corresponding one of the plurality of patterned optical output components at a distance defined by:   x  =            f      2        +                  1        4            ·                                    4            ·                          f              2                                -                                                    π                2                            ·                              do                4                                                    λ              2                                          
wherein f is the effective focal length of the corresponding one of the plurality of patterned optical output components, do is a Gaussian mode field diameter of the optical output fiber, and xcex is the wavelength associated with the narrowband optical beam being transmitted to the optical output fiber. Accordingly, the distance between each of the plurality of optical output fibers and each corresponding one of the plurality of patterned optical output components may vary with wavelength. Alternatively, the effective focal length of each of the plurality of patterned optical output components may differ so that the distance between each of the plurality of optical output fibers and each corresponding one of the plurality of patterned optical output components does not vary with wavelength.
In accordance with still further aspects of the present invention, the optical source is beneficially an optical input fiber, wherein the multiplexed, polychromatic optical beam is received from the optical input fiber. The optical input fiber is beneficially disposed from the corresponding patterned optical input component at a distance defined by:   x  =            f      2        +                  1        4            ·                                    4            ·                          f              2                                -                                                    π                2                            ·                              do                4                                                    λ              2                                          
wherein f is the effective focal length of the corresponding patterned optical input component, do is a Gaussain mode field diameter of the optical input fiber, the xcex is the average wavelength associated with the multiplexed, polychromatic optical beam being received from the optical input fiber.
In accordance with other aspects of the present invention, the patterned optical input component beneficially comprises a patterned phase mask for introducing the first patterned phase delay into the multiplexed, polychromatic optical beam. The patterned phase mask is preferably formed on/in a collimating microlens. Alternatively, the patterned optical output component also beneficially comprises a collimating microlens for collimating the multiplexed, polychromatic optical beam. In either case, the collimating microlens contributes to a widening of the passband of the improved wavelength division demultiplexing device.
In accordance with further aspects of the present invention, the patterned phase mask beneficially has a periodic phase profile. A benefit of this aspect is that the passband of the improved wavelength division demultiplexing device is a gaussian-shaped passband having a peak, and the periodic phase profile of the patterned phase mask contributes to a flattening of the peak of the gaussian-shaped passband of the improved wavelength division demultiplexing device. Another benefit to this aspect is that the passband of the improved wavelength division demultiplxing device is a guassian-shaped passband having sideband slopes, and the periodic phase profile of the patterned phase mask contributes to a steepening of the sideband slopes of the gaussian-shaped passband of the improved wavelength division demultiplexing device.
In accordance with still further aspects of the present invention, the patterned phase mask beneficially has a non-periodic phase profile. A benefit to this aspect is that the passband of the improved wavelength division demultiplexing device is a gaussian-shaped passband having a peak, and the non-periodic phase profile of the patterned phase mask contributes to a flattening of the peak of the gaussian-shaped passband of the improved wavelength division demultiplexing device. Another benefit to this aspect is that the passband of the improved wavelength division demultiplexing device is a guassian-shaped passband having sideband slopes, and the non-periodic phase profile of the patterned phase mask contributes to a steepening of the sideband slopes of the gaussian-shaped passband of the improved wavelength division demultiplexing device.
In accordance with other aspects of the present invention, the plurality of patterned optical output components beneficially comprises a plurality of patterned phase masks for introducing the second patterned phase delay into the plurality of narrowband optical beams. Each of the plurality of patterned phase masks is preferably formed on/in a corresponding focusing microlens. Alternatively, the plurality of patterned optical output components also beneficially comprises a plurality of focusing microlenses for focusing the plurality of narrowband optical beams. In either case, each corresponding focusing microlens or each of the plurality of focusing microlenses contributes to a widening of the passband of the improved wavelength division demultiplexing device.
In accordance with further aspects of the present invention, each of the plurality of patterned phase masks beneficially has a periodic phase profile. A benefit to this aspect is that the passband of the improved wavelength division demultiplexing device is a guassian-shaped passband having a peak, and the periodic phase profile of each patterned phase mask contributes to a flattening of the peak of the gaussian-shaped passband of the improved wavelength division demultiplexing device. Another benefit to this aspect is that the passband of the improved wavelength division demultiplexing device is a gaussian-shaped passband having sideband slopes, and the periodic phase profile of each patterned phase mask contributes to a steepening of the sideband slopes of the gaussian-shaped passband of the improved wavelength division demultiplexing device.
In accordance, with still further aspects of the present invention, each of the plurality of patterned phase masks beneficially has a non-periodic phase profile. A benefit to this aspect is that the passband of the improved wavelength division demultiplexing device is a gaussian-shaped passband having a peak, and the non-periodic phase profile of each patterned phase mask contributes to a flattening of the peak of the gaussian-shaped passband of the improved wavelength division demultiplexing device. Another benefit to this aspect is that the passband of the improved wavelength division demultiplexing device is a guassian-shaped passband having sideband slopes, and the non-periodic phase profile of each patterned phase mask contributes to a steepening of the sideband slopes of the gaussian-shaped passband of the improved wavelength division demultiplexing device.